Net Interest Income - Components of Interest Revenue and Interest Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Banking and Thrift [Abstract]
Interest-bearing deposits with banks	$ 109	$ 90	$ 228	$ 172
U.S. Treasury and federal agencies	360	280	729	534
State and political subdivisions	13	44	25	96
Other investments	126	140	248	298
Securities purchased under resale agreements	90	81	188	159
Loans and leases	195	169	393	325
Other interest-earning assets	114	103	223	180
Total interest income	1,007	907	2,034	1,764
Interest-bearing deposits	209	89	380	152
Securities sold under repurchase agreements	8	6	20	7
Other short-term borrowings	6	4	10	7
Long-term debt	107	97	213	194
Other interest-bearing liabilities	64	52	125	102
Total interest expense	394	248	748	462
Net interest income	$ 613	$ 659	$ 1,286	$ 1,302